JP2010190636A - Acceleration sensor - Google Patents

Abstract

An acceleration sensor is provided which has excellent impact resistance and suppresses a decrease in acceleration detection characteristics.
Since the damping structure 80 is provided in addition to the fixed electrode 41 and the movable electrode 21, the damping structure 80 adjusts the damping without reducing the inter-electrode gap 70 between the fixed electrode 41 and the movable electrode 21. Can do. Therefore, the collision failure between the movable part 20 and the support 10 is reduced, the impact resistance is excellent, the acceleration can be detected while avoiding the collision between the fixed electrode 41 and the movable electrode 21, and the acceleration detection characteristic is deteriorated. A small number of acceleration sensors 100 can be obtained.
[Selection] Figure 1

Description

  The present invention relates to an acceleration sensor that detects acceleration based on a change in capacitance between a fixed electrode and a movable electrode.

As an acceleration sensor, an acceleration sensor that detects acceleration based on a change in capacitance between a fixed electrode and a movable electrode provided on a support is known. The movable electrode is formed in a movable part having a weight, and the movable part is connected to the support body by a spring. In such an acceleration sensor, it is possible to detect acceleration having a component in the direction in which the capacitance between the fixed electrode and the movable electrode changes.
The structural resonance frequency of the acceleration sensor having the above-described structure is uniquely determined from the mass m of the movable part and the spring constant k. Further, the Q value indicating the sharpness of resonance is determined from a calculation formula obtained by adding the damping constant c to the mass m of the movable part and the spring constant k, and is inversely proportional to the damping constant c.
The acceleration sensor is required to have a low Q value in terms of transient response and impact resistance. For example, a Q value of about 0.5 to 1.0 is required. Since the structural resonance frequency of the acceleration sensor is determined by the structure, the Q value is designed in consideration of the damping (damping force) represented by the damping constant c due to the interaction between the support, the movable part, etc. and the gas surrounding them. Is done. As the damping constant c increases, the Q value decreases.
As a method of reducing the Q value, the distance between the movable body that is the movable portion and the support substrate that is the support body is narrowed, and slide damping that occurs when the movable body and the support substrate are displaced is utilized, and the damping that is the damping constant c A method for increasing the coefficient is known (see Patent Document 1).

JP 2004-286649 A (pages 3 to 4, FIG. 1)

However, if the distance between the movable part and the support is reduced, the impact between the movable part and the support causes a collision failure between the movable part and the support, resulting in a reduction in impact resistance.
Further, in the dumping using the gap between the fixed electrode and the movable electrode, it is necessary to narrow the gap between the fixed electrode and the movable electrode. In this case, the fixed electrode and the movable electrode come into contact with each other due to the electrostatic force, or it becomes difficult to ensure linearity due to the electrostatic force, so that the acceleration detection characteristic is deteriorated.

  SUMMARY An advantage of some aspects of the invention is to solve at least one of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A support, a fixed electrode formed on the support, a first damping structure formed on the support, a movable part, a movable electrode provided on the movable part, and the movable part And the fixed electrode and the movable electrode are arranged opposite to each other with a first gap therebetween to form a capacitance, and the first damping structure and the second damping structure are provided. An acceleration sensor, wherein the damping structure is disposed to face the second structure with a second gap therebetween.

  According to this application example, since the damping structure composed of the first damping structure and the second damping structure is provided in addition to the fixed electrode and the movable electrode, the damping structure is made without narrowing the first gap. Damping can be adjusted by the second gap of the body. Therefore, there is an acceleration sensor that reduces collision failure between the movable part and the support body, has excellent impact resistance, can detect acceleration while avoiding collision between the fixed electrode and the movable electrode, and has little deterioration in acceleration detection characteristics. can get.

[Application Example 2]
The acceleration sensor according to claim 1, wherein the second gap is narrower than the first gap.
In this application example, the second gap can be made narrower than the first gap to increase the damping.

[Application Example 3]
The acceleration sensor according to claim 1, wherein the fluctuation direction of the first gap and the fluctuation direction of the second gap substantially coincide with each other.
In this application example, since the fluctuation direction of the first gap and the fluctuation direction of the second gap substantially coincide, the damping force efficiently acts on the fluctuation of the second gap between the fixed electrode and the movable electrode.

[Application Example 4]
In the acceleration sensor, a plurality of the first damping structures and the second damping structures are respectively formed, and are symmetric with respect to the fluctuation direction of the first gap or the center of gravity of the movable portion. An acceleration sensor characterized by being arranged.
In this application example, the first damping structure and the second damping structure are arranged symmetrically with respect to the fluctuation direction of the first gap or the center of gravity of the movable part. The damping force works evenly, and the sensitivity in other directions is suppressed.

[Application Example 5]
In the acceleration sensor, the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure have a stacked structure used in an integrated circuit. A characteristic acceleration sensor.
In this application example, since the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure are laminated, the acceleration sensor can be formed on the substrate on which the integrated circuit is formed.

[Application Example 6]
The acceleration sensor, wherein the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure are made of single crystal silicon. sensor.
In this application example, since the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure are made of single crystal silicon, deformation due to thermal stress is small, and the thick structure Formation is also easy.

(A) in 1st Embodiment is a schematic plan view of an acceleration sensor, (b) is AA schematic sectional drawing in (a). The schematic sectional drawing of a manufacturing process in the case of forming a CMOS integrated circuit and an acceleration sensor in a board | substrate. (A) in 2nd Embodiment is a schematic plan view of an acceleration sensor, (b) is AA schematic sectional drawing in (a). The schematic sectional drawing of a manufacturing process in the case of forming a CMOS integrated circuit and an acceleration sensor in a board | substrate. The schematic plan view of the acceleration sensor in a modification.

Hereinafter, embodiments will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a schematic diagram of an acceleration sensor 100 in the present embodiment. (A) is a schematic plan view of the acceleration sensor 100, (b) is an AA schematic sectional drawing in (a). In the figure, the X, Y, and Z axis directions are shown. Also, the double arrows in the figure indicate the acceleration detection direction, and in the present embodiment, the X-axis direction is the acceleration detection direction.

In FIG. 1, the acceleration sensor 100 includes a support 10 and a movable part 20.
The support 10 includes a substrate 30 and a support portion 40 formed on the substrate 30. The movable part 20 is also formed on the substrate 30.
The substrate 30 is made of a silicon substrate, and a concave portion 31 is formed on the surface of the substrate 30 that faces the movable portion 20 in order to provide a gap between the substrate 30 and the movable portion 20. The depth of the recess 31 is such that the impact does not occur even when the impact is applied in the Z-axis direction of the movable portion 20 and the movable portion 20 is bent toward the substrate 30 side.

The movable unit 20 and the support unit 40 include, for example, a wiring layer 50, an interlayer insulating film 60, and the like that constitute a CMOS (Complementary Metal Oxide Semiconductor) integrated circuit 400 as an integrated circuit described later formed in another region on the substrate 30. It is formed using the laminated structure which consists of.
As the wiring layer 50, for example, Al, Cu, Al alloy, Mo, Ti, W, Pt, or the like can be used. The wiring layer 50 includes a barrier film made of TiN, Ti, TiW, TaN, WN, VN, ZrN, NbN, or the like used when forming the CMOS integrated circuit 400, or an antireflection film made of TiN, Ti, or the like. . The wiring layer 50 also includes a CMOS gate electrode. The gate electrode is made of polycrystalline silicon containing impurities, silicide, W, or the like.
The interlayer insulating film _{60, SiO 2, TEOS (Tetraethoxysilane} ), BPSG (Borophosphosilicate Glass), NSG (Non-doped silicon glass), can be used SOG (Spin on glass) or the like. The laminated structure may include a protective film made of SiN, SiO ₂ or the like formed on the outermost surface of the CMOS integrated circuit 400.

The wiring layer 50 of Al or the like can be formed by sputtering, vacuum deposition, CVD (Chemical Vapor Deposition) or the like, and the interlayer insulating film 60 of SiO ₂ or the like can be formed by CVD, thermal oxidation, spin coating, baking, or the like. .
In addition, the movable part 20 and the support part 40 are not limited to those formed using the stacked structure of the CMOS integrated circuit 400, but may be formed by independently forming a stacked structure.

The support part 40 is formed on the substrate 30 as a substantially rectangular frame. The support unit 40 includes a fixed electrode 41. The fixed electrode 41 is formed in the approximate center of one opposing inner surface of the support portion 40 toward the inside of the frame. The shape of the fixed electrode 41 is a plate-shaped rectangular parallelepiped.
The movable portion 20 includes a movable electrode 21, a weight portion 22, and spring portions 23 and 24. The shape of the weight part 22 is formed in a substantially rectangular parallelepiped. The movable portion 20 is located at the approximate center surrounded by the support portion 40 that is a substantially rectangular frame body via the inner surfaces of the remaining pair of support bodies where the fixed electrode 41 is not formed and the two spring portions 23 and 24. It is held in two places.
The spring parts 23 and 24 have a structure in which two opposing leaf springs face each other and are fixed at both ends. Of the two leaf springs, one leaf spring is connected to the support portion 40, and the other leaf spring is connected to the weight portion 22.

The movable electrode 21 is formed at a position facing the fixed electrode 41 of the weight portion 22. The movable electrode 21 is also a plate-like rectangular parallelepiped like the fixed electrode 41.
The movable electrode 21 and the fixed electrode 41 are opposed to each other via an inter-electrode gap 70 as a first gap having a distance a so that a capacitance can be obtained between the electrodes.

  The acceleration sensor 100 includes a damping structure 80. In the present embodiment, damping structures 80 are provided on both sides so as to sandwich the opposed movable electrode 21 and fixed electrode 41, and damping structures 80 are provided at a total of four locations. The damping structure 80 is disposed at a symmetrical position with respect to the fluctuation direction of the interelectrode gap 70.

The damping structure 80 includes a fixed body 42 as a first damping structure and a movable body 25 as a second damping structure.
The movable body 25 is formed toward the support portion 40 on both sides of the movable electrode 21 of the weight portion 22. On the other hand, the fixed body 42 is formed on both sides of the fixed electrode 41 of the support portion 40 at positions facing the movable body 25 with a gap 90 as a second gap having a distance b. Here, the interval a is set larger than the interval b.

Although the size of each component in the case of forming the acceleration sensor 100 on the board | substrate 30 with the CMOS integrated circuit 400 is not specifically limited, For example, it is as follows.
The thickness of the laminated structure of the movable part 20 and the support part 40 is about several μm, and the support part 40 is a frame of about several mm square. Each layer of the laminated structure is about 1 μm. The distance a of the interelectrode gap 70, which is the distance between the movable electrode 21 and the fixed electrode 41, is about several μm. Further, the mass of the weight portion 22 is about several × 10 ⁻⁶ g.

The movable part 20 and the support part 40 can be formed by combining anisotropic etching and isotropic etching from the surface side of the laminated structure composed of the wiring layer 50 and the interlayer insulating film 60.
FIGS. 2A to 2C are simplified sectional views showing a manufacturing process in the case where the CMOS integrated circuit 400 and the acceleration sensor 100 are formed on the substrate 30 as an example.
2A shows a process of forming the CMOS integrated circuit 400 and the acceleration sensor unit 110 before etching, FIG. 2B shows an anisotropic etching process of the interlayer insulating film 60 and the like, and FIG. The isotropic etching process is shown.

In FIG. 2A, an impurity diffusion layer 411, a source 412, a drain 413, a LOCOS (Local Oxidation of Silicon) 414, a gate oxide film 415, a gate 416, and the like constituting the transistor 410 are formed on the substrate 30, and then on the transistor 410. Then, the plug 420, the wiring layer 50, the interlayer insulating film 60, the protective film 430, and the like are laminated, and etching is repeated to form the CMOS integrated circuit 400 by a known method.
At this time, the LOCOS 414, the gate oxide film 415, the gate 416, and the like are formed in the acceleration sensor unit 110 before etching, and the interlayer insulating film 60, the wiring layer 50, the protective film 430, and the like are stacked thereon.

In FIG. 2B, anisotropic etching of the interlayer insulating film 60 and the like is performed from the protective film 430 side. The anisotropic etching is performed by, for example, ICP (Inductively Coupled Plasma) etching. As an etching gas, a mixed gas such as CF ₄ , CH ₃ , and He is used, and the pressure is 10 to 20 Pa and the RF power is 600 to 800 W. The etching time is 10 to 20 minutes when the total film thickness of the protective film 430 and the interlayer insulating film 60 is 4 to 6 μm.

In FIG. 2C, isotropic etching of the silicon substrate 30 is performed from the protective film 430 side to form the recesses 31. The isotropic etching is performed by, for example, ICP (Inductively Coupled Plasma) etching. As the etching gas, a mixed gas of SF ₆ and O ₂ is used, and the pressure is 1 to 100 Pa and the RF power is about 100 W. The etching time is several minutes when the depth of the recess 31 is 2 to 3 μm. By this etching, the movable part 20 and the like are separated from the substrate 30.

  In the acceleration sensor 100, when acceleration is applied in the X-axis direction, the distance between the fixed electrode 41 and the movable electrode 21 changes and the capacitance changes. By detecting this change in capacitance, the acceleration can be measured.

According to this embodiment, there are the following effects.
(1) Since the damping structure 80 is provided in addition to the fixed electrode 41 and the movable electrode 21, the damping structure 80 can adjust the damping without reducing the inter-electrode gap 70 between the fixed electrode 41 and the movable electrode 21. it can. Therefore, the collision failure between the movable part 20 and the support 10 is reduced, the impact resistance is excellent, the acceleration can be detected while avoiding the collision between the fixed electrode 41 and the movable electrode 21, and the acceleration detection characteristic is deteriorated. A small number of acceleration sensors 100 can be obtained.

  (2) Damping is performed by setting the gap b of the gap 90 between the movable body 25 and the fixed body 42 of the damping structure 80 to be smaller than the gap a of the gap 70 between the fixed electrode 41 and the movable electrode 21. Can be bigger.

  (3) Since the fluctuation direction of the gap 90 and the fluctuation direction of the inter-electrode gap 70 are substantially the same, the damping force works efficiently on the fluctuation of the inter-electrode gap 70 between the fixed electrode 41 and the movable electrode 21. it can.

  (4) Since the damping structure 80 is arranged symmetrically with respect to the fluctuation direction of the gap 90 or the center of gravity of the movable portion 20, a damping force acts evenly with respect to the fluctuation direction of the gap 90 and moves in the other direction. The sensitivity of can be suppressed.

  (5) Since the fixed electrode 41, the movable electrode 21, the movable portion 20, and the damping structure 80 have a laminated structure, the acceleration sensor 100 can be formed on the substrate 30 on which the CMOS integrated circuit 400 is formed.

(Second Embodiment)
FIG. 3 shows a schematic diagram of the acceleration sensor 200 in the present embodiment. (A) is a schematic plan view of the acceleration sensor 200, (b) is an AA schematic sectional drawing in (a). In the figure, the axial direction is shown. The double arrows in the figure indicate the acceleration detection direction. In the present embodiment, the X-axis direction is the acceleration detection direction.
The same components as those in the first embodiment are denoted by the same reference numerals. Below, it demonstrates centering on a different point from 1st Embodiment.

In FIG. 3, the structure of the acceleration sensor 200 is substantially the same as the acceleration sensor 100 shown in the first embodiment. The difference in structure is that the damping structure 80 is provided only on one side, not on both sides of the movable electrode 21 and the fixed electrode 41 facing each other.
The damping structure 80 is disposed at 2 l positions symmetrical with respect to the center of gravity 221 of the movable portion 20.

The first embodiment and the second embodiment are greatly different in the following points.
In the first embodiment, the substrate 30 is made of a silicon substrate, and the support portion 40 and the movable portion 20 are the wiring layer 50 and the interlayer insulating film that constitute the CMOS integrated circuit 400 formed in another region on the substrate 30. A laminated structure using 60 is used. On the other hand, in the second embodiment, a semiconductor substrate 35 having an SOI (Silicon On Insulator) structure is used. The SOI structure includes a single crystal silicon layer 220 formed on a buried oxide film with a buried oxide film 210 made of silicon oxide interposed therebetween.

The movable part 20 and the support part 40 are obtained by etching the single crystal silicon layer 220. Further, the through portion 32 of the substrate 30 can be formed by etching from a surface facing the surface on which the single crystal silicon layer 220 is formed.
4A to 4C show, as an example, a simplified manufacturing process in the case where the CMOS integrated circuit 400 and the acceleration sensor 200 are formed on the semiconductor substrate 35 having an SOI structure.
4A shows a process of forming the CMOS integrated circuit 400, FIG. 4B shows an anisotropic etching process of the single crystal silicon layer 220 from the surface where the CMOS integrated circuit 400 is formed, and FIG. The anisotropic etching process from the board | substrate 30 side is shown.

  In FIG. 4A, as in the first embodiment, a CMOS integrated circuit 400 is formed on the single crystal silicon layer 220 by a known method. At this time, nothing is formed in the acceleration sensor unit 110.

In FIG. 4B, anisotropic etching is performed from the surface of the single crystal silicon layer 220 where the CMOS integrated circuit 400 is formed. The anisotropic etching can be performed by wet etching with KOH after applying a mask according to the shape of the acceleration sensor 200 with SiO ₂ or the like.

  In FIG. 4C, the substrate 30 and the buried oxide film 210 are etched from the substrate 30 side to form the penetrating portion 32, and then anisotropic etching is performed from the substrate 30 side. The anisotropic etching can be performed by a method similar to the method performed from the side of the single crystal silicon layer 220 where the CMOS integrated circuit 400 is formed.

According to this embodiment, there are the following effects.
(6) Since the fixed electrode 41, the movable electrode 21, the movable portion 20, and the damping structure 80 are made of single crystal silicon, deformation due to thermal stress can be reduced and a thick structure can be easily formed.

(Modification)
FIG. 5 shows a schematic plan view of an acceleration sensor 300 according to a modification.
In FIG. 5, the difference from the first and second embodiments is that the movable electrode 26 that detects acceleration in the Y-axis direction in addition to the movable electrode 21 and fixed electrode 41 that detect acceleration in the X-axis direction. The difference is that a fixed electrode 43 is provided and a damping structure 80 is provided on both sides of these electrodes. Further, the movable electrode 21 and the fixed electrode 41, and the movable electrode 26 and the fixed electrode 43 are not a differential detection type.
Regarding the structure and manufacturing method other than those described above, the same laminated structure as that of the first embodiment, the same structure as that of the second embodiment, and the same manufacturing method as that of the first and second embodiments can be used.
In the modification, acceleration in two directions can be measured.

Various modifications other than the above-described embodiment can be made.
The spring portions 23 and 24 may have any structure. For example, a structure in which both ends of one leaf spring are connected to the support portion 40 and the center portion is connected to the weight portion 22 may be employed.

In the embodiment, only two pairs of the movable electrode 21 and the fixed electrode 41 are shown, but a configuration in which comb teeth are inserted in three pairs or more may be employed. The movable electrode 21 and the fixed electrode 41 have a structure in which rectangular electrodes face each other, but may have a shape other than a rectangular shape.
Further, if the electrodes do not collide by application of acceleration, they may not be parallel plates.

  Furthermore, the gas may be a rare gas such as He or Ne other than air, a nitrogen gas, or the like. By using a medium having a viscosity coefficient larger than that of air, a larger damping constant c can be obtained.

  The damping structure 80 may change not only the distance b of the gap 90 between the movable body 25 and the fixed body 42 but also the shapes of the movable body 25 and the fixed body 42. In addition, although only two and four pairs of the movable body 25 and the fixed body 42 are shown, a configuration in which comb teeth are included in six pairs or more may be employed.

  DESCRIPTION OF SYMBOLS 10 ... Support body, 20 ... Movable part, 21 ... Movable electrode, 25 ... Movable body as 2nd damping structure, 41 ... Fixed electrode, 42 ... Fixed body as 1st damping structure, 70 ... 1st Interelectrode gap as a gap, 90... Second gap, 100, 200, 300... Acceleration sensor, 400... CMOS integrated circuit, 220... Single crystal silicon layer as single crystal silicon, 221.

Claims (6)

A support;
A fixed electrode formed on the support;
A first damping structure formed on the support;
Moving parts;
A movable electrode provided in the movable part;
A second damping structure provided on the movable part,
The fixed electrode and the movable electrode are opposed to each other with a first gap therebetween to form a capacitor,
The first damping structure and the second damping structure are arranged to face each other with a second gap therebetween. The acceleration sensor according to claim 1,
The acceleration sensor, wherein the second gap is narrower than the first gap. The acceleration sensor according to claim 2,
The acceleration sensor characterized in that the fluctuation direction of the first gap substantially coincides with the fluctuation direction of the second gap. In the acceleration sensor according to any one of claims 1 to 3,
A plurality of the first damping structures and the second damping structures are formed and arranged at positions symmetrical with respect to the direction of variation of the first gap or the center of gravity of the movable part. An acceleration sensor. In the acceleration sensor according to any one of claims 1 to 4,
The acceleration sensor, wherein the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure have a laminated structure used in an integrated circuit. In the acceleration sensor according to any one of claims 1 to 4,
The acceleration sensor, wherein the fixed electrode, the movable electrode, the movable portion, the first damping structure, and the second damping structure are made of single crystal silicon.

Images